Neuropeptides
A neuropeptide is any of the variety of peptides found in neural tissue; e.g. endorphins, enkephalins. Now, about 100 different peptides are known to be released by different populations of neurons in the mammalian brain. Neurons use many different chemical signals to communicate information, including neurotransmitters, peptides, cannabinoids, and even some gases, like nitric oxide. Many populations of neurons have distinctive biochemical phenotypes. For example, in one subpopulation of about 3000 neurons in the arcuate nucleus of the hypothalamus, three anorectic peptides are co-expressed: α-melanocyte-stimulating hormone (α-MSH), galanin-like peptide, and cocaine-and-amphetamine-regulated transcript (CART), and in another subpopulation two orexigenic peptides are co-expressed, neuropeptide Y and agouti-related peptide (AGRP). These are not the only peptides in the arcuate nucleus; β-endorphin, dynorphin, enkephalin, galanin, ghrelin, growth-hormone releasing hormone, neurotensin, neuromedin U, and somatostatin are also expressed in subpopulations of arcuate neurons. These peptides are all released centrally and act on other neurons at specific receptors. The neuropeptide Y neurons also make the classical inhibitory neurotransmitter GABA. Invertebrates also have many neuropeptides. CCAP has several functions including regulating heart rate, allatostatin and proctolin regulate food intake and growth, bursicon controls tanning of the cuticle and corazonin has a role in cuticle pigmentation and moulting. Peptide signals play a role in information processing that is different from that of conventional neurotransmitters, and many appear to be particularly associated with specific behaviours. For example, oxytocin and vasopressin have striking and specific effects on social behaviours, including maternal behaviour and pair bonding. Function Generally, peptides act at metabotropic or G-protein-coupled receptors expressed by selective populations of neurons. In essence they act as specific signals between one population of neurons and another. Neurotransmitters generally affect the excitability of other neurons, by depolarising them or by hyperpolarising them. Peptides have much more diverse effects; amongst other things, they can affect gene expression, local blood flow, synaptogenesis, and glial cell morphology. Peptides tend to have prolonged actions, and some have striking effects on behaviour. Neurons very often make both a conventional neurotransmitter (such as glutamate, GABA or dopamine) and one or more neuropeptides. Peptides are generally packaged in large dense-core vesicles, and the co-existing neurotransmitters in small synaptic vesicles. The large dense-core vesicles are often found in all parts of a neuron, including the soma, dendrites, axonal swellings and nerve endings, whereas the small synaptic vesicles are mainly found in clusters at presynaptic locations. Release of the large vesicles and the small vesicles is regulated differentially. Examples Following is a list of neuroactive peptides coexisting with other neurotransmitters. Transmitter names are shown in bold. Norepinephrine (noradrenaline). In neurons of the A2 cell group in the nucleus of the solitary tract), norepinephrine co-exists with: * Galanin * Enkephalin * Neuropeptide Y GABA * Somatostatin (in the hippocampus) * Cholecystokinin * Neuropeptide Y (in the arcuate nucleus) Acetylcholine * VIP * Substance P Dopamine * Cholecystokinin * Neurotensin Epinephrine (adrenaline) * Neuropeptide Y * Neurotensin Serotonin (5-HT) * Substance P * TRH * Enkephalin Some neurons make several different peptides. For instance, Vasopressin co-exists with dynorphin and galanin in magnocellular neurons of the supraoptic nucleus and paraventricular nucleus, and with CRF (in parvocellular neurons of the paraventricular nucleus) Oxytocin in the supraoptic nucleus co-exists with enkephalin, dynorphin, cocaine-and amphetamine regulated transcript (CART) and cholecystokinin. By site Pituitary peptides *Corticotropin *Growth hormone *Lipotropin *Melanocyte stimulating hormone *Oxytocin *Prolactin *Vasopressin Gut peptides *Cholecystokinin *Gastrin *Motilin *[[Pancreatic polypeptide *Secretin *Substance P *Vasoactive intestinal polypeptide Hypothalamic peptides *Luteinizing hormone-releasing hormone *[[Somatostatin *Thyrotropin-releasing hormone Endorphins *Dynorphin *Beta-endorphine *Met encephalin *Leu enkephalin Miscellaneous *Angiotensin *Bombesin *Bradykinin *Carnosine *Glucagon *Insulin *Neuropeptide Y *Neurotensin *Proctolin Diabetes link A new discovery might have important implications for treatment of diabetesT1DM, diabetes and trpv1 / capsaicin,TRPV1+ Sensory Neurons Control Cell Stress and Islet Inflammation in Autoimmune Diabetes. Researchers at the Toronto Hospital for Sick Children injected capsaicin into NOD mice (Non-obese diabetic mice, a strain that is genetically predisposed to develop the equivalent of type 1 diabetes) to kill the pancreatic sensory nerves. This treatment reduced the development of diabetes in these mice by 80%, suggesting a link between neuropeptides and the development of diabetes. When the researchers injected the pancreas of the diabetic mice with substance P, they were cured of the diabetes for as long as 4 months. Also, insulin resistance (characteristic of type 2 diabetes) was reduced. These research results are in the process of being confirmed, and their applicability in humans will have to be established in the future. Any treatment that could result from this research is probably years away. See also *Calcitonin gene-related peptide References External links * [http://www.intl.elsevierhealth.com/journals/npep/ Neuropeptides Journal] * Neuropeptides reference website See also *Candace Pert Category:Molecular biology Category:Neuropeptides